A typical preparative LC using the HPLC is shown in FIG. 5. The eluent (or the “moving phase”) in the eluent tank 1 is drawn by a pump 2 and is sent at a constant flow rate to the column 4 via the sample injector 3. The sample injected at the sample injector 3 is carried by the eluent to the column 4, where the components of the sample are separated in the course of time. The separated components flow out of the other end of the column 4 one after another. The detector 5 (“UV detector” in FIG. 5) detects the components flowing out of the column 4, and sends corresponding signals to the signal processor 6. All of or a part of the eluate passing through the detector 5 is introduced into the fraction collector 8. The signal processor 6 generates a chromatogram based on the signals sent from the detector 5, and the separation controller 7 sends signals to the fraction collector 8 based on the peaks appearing in the chromatogram. According to the signals from the separation controller 7, the fraction collector 8 operates the control valves to the respective vials to batch off (or separate) the components.
For the detector of many kinds of preparative LCs, the ultraviolet-visible light spectrophotometer (“UV detector”) using a photodiode array detector has been widely used. Recently, though, a mass spectrometer (“MS”) has begun to be used as the detector. When an MS is used, the components contained in the sample are detected with their mass to charge ratios, which enables the separation of components even if they have the same or close retention time of the liquid chromatograph. Thus, by using the liquid chromatograph mass spectrometer (LCMS) including an MS as the detector, it is possible to batch off components more accurately than before.
FIG. 6 shows a schematic structure of a preparative LC using an MS as the detector. Same or similar elements to those in FIG. 5 are labeled the same, and the description above is applied the same as above. Since, in the MS 9, the components of the sample to be detected are ionized, the eluent is consumed there, which means that it is impossible to separate the eluate that has passed through the MS 9. Instead of this being a drawback, it has the advantage that the amount of eluate necessary for the detector 9 is very small. Thus, the current LCMS adopts the following structure. A splitter 11 is provided between the column 4 and the MS 9, and only a very small part of the eluate flowing out of the column 4 of the liquid chromatograph is given to the MS 9, while most of the rest of the eluate is sent to the fraction collector 8.
In many HPLCs, a so-called multiple detection system is adopted in which an UV detector or an evaporation light scattering detector (ELSD) is used as well as the MS detector. Such a system is adopted because a single detector cannot cover all the object components. Respective detectors used in a multiple detection system detect an appropriate component or components, and they complementarily detect all the components contained in a sample. This improves the detection accuracy and prevents any detection miss. Such a multiple detection system is presumed to be also useful for the preparative LC using the fraction collector. But in conventional preparative LCs using the multiple detection system, the separation of components of a sample is performed based on the detection signals of the plural detectors, where the detection signals are chosen arbitrarily. Thus the advantage of the multiple detection system as described above is not fully realized.